Process of burning ceramic ware.



H. L. DOHERTY.

PROCESS OF BURNING CERAMIC WARE. APPLICATION FILED OCT. 29, I909- RENEWED FEB. 7,1916.

1,175,246. Patented Mar. 14, 1916.

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WWW-0M0: Henry oherty, woawtoz THE COLUMBIA PL IUGRAPH 60-, WASHINGTON, D. c.

2 SHEETSSHEET 2- 5 s Qwws 45 wp is Patented Mar. 14, 1916.

H. L. DOHERTY.

PROCESS OF BURNING CERAMIC WARE. APPLICATION FILED OCT. 29, 1909. RENEWED FEB. 7. 1916.

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. UNITED STATES PATENT ouuicu.

HENRY L. DOHERTY, or NEWVYORK, 1v. 3!.

PROCESS OF BURNING CERAMIC WAR-E.

Specification of Letters Patent.

' Patented Mar. 14, 1916.

Application filed October 29, 1909, Serial No. 525,390. Renewed February 7, 1916. Serial No. 76,773.

To all whom it may concern:

Be it known that I, HENRY L. DOHERTY, a citizen of the United States, and a resident of New York city, in the 'county of New York and State of New York, havevinvented certain new and useful Improvements in Processes of Burning Ceramic are, of which the following is a specification.

ware is subjected to a preliminary drying, gradually heated up to the burning tern:

perature by a current ofgas of gradually increasing temperature, burned by a flame of modified producer-gas of regulated temperature, and subjected to a gradual cooling bya current of air of gradually decreasing temperature, whereby I am able to secure ware of better and more uniform quality than it is possible to secure by present methods of burning, and at the same time, owing to the practically perfect heat recuperation which I secure, burn the ware with afraction of the quantity of fuel that is required in the, atpresent, known methods of burning.

'In the apparatus for carrying out my invention which I herein describe, Figure 1 is a vertical cross-section through one ofthe individual shafts or kilns on thelines IJ of Fig. 2, and MNof Fig. 6. Fig. 2 is a vertical cross-section at right angles to the one in Fig. 1, on the line AB of Fig. 1, and

KL of Fig. 6. Fig. 3 is elevation (dia-' grammatic) of the brick or tile press, and

elevator for raising the molded ware to the charging platform of the kilns. Fig. 4 is a detail of the elevator. Fig. 5 a detail of the gear actuating the discharging contrivance at the top of the kiln. Fig. 6 is a art to view of a battery of kilns. Fig. is

, a part horizontal section through the battery of kilns on a planethrough the line EF of Fig.1 at thelevelof the gas ports Fig.

fresh lot of bricks.

the line GI-I of Fig. 1, at the level of the air inletsand the false bars supporting'the charge in the kiln.

The construction and ing my apparatus areas follows The bricks or tiles, as the case may be,

are molded in-the ordinary manner by the method of operati press '1, and emerge onto a palletboardoQ, .i- .1

on the cutting table 3. By operating the lever a, the bricks are cut to the proper size and the pallet on which they rest moved to one side on the arms 5, while an empty pallet, 2,'is placed in position to receive a i.'

I The charged pallet is next lifted from the carriers 5 by the projectingarins 6 of elevator '7. This be of any suitable design, the device shown consisting of a sprocket chain 8, having links 9, bearing the arms 6, connected with each other by the solid links 10. The chains 8 work in suitable guides 11, and over pairs ofsuitable sprocket wheels 12 and 12', re-

spectively, of which 12 are-the driving wheels.- The loaded pallets supported by the arms 6 are raised tothe level of'the charging platform 13, at the top of the kilns. Here they are lifted from the elevator by a contrivance, 1 1. The contrivance here shown has two arms, 15, 15, mounted on a shaft 16, which shaft carries a mutilated gear 17. This meshes into a corresponding gear wheel'17" on the shaft i18. '18 has-a pulley 19, which'is connected j by the belt 20 with a pulley 21 on the axle 22 of the sprocket wheels 12. The gear wheels are of such relative diametersthat the gear 17 rotates through, say, 105 de-- grees while the gear 17 rotates through a lesser arc of, say, 30 degrees or' more. The arms 15 are so weighted that upon the disengagement of the gears 17-17 theywill drop to a vertical position, thereby rotating the toothed'portion of the periphery of thegear wheel 17"back into a position from f which it can again engage the gear 17 when the toothed portion of the latter again comes into the-proper position on the further rotationof the sprocket wheels' These latter should be of such diameter that their cirv c'umferenceis equal to the interval between the arms 6 on the chains. By this device as each pallet with its load of bricks,.;.or other ware, approaches the position cm, the arms or rotatable skids 15 are caused. to rotate, passing upward between the arms 6 of elevator 7, lifting the pallet off of the elevator. As the arms 15 approach their upper position the pallet slides down them by gravity and onto the moving belt conveyer 23, by which it is conveyed to whatever kiln is, at the time, being charged, where it is lifted off the belt by a workman and the bricks which it carries builtonto the column of bricks in the kiln after the manner hereinafter described.

The kilns are arranged in batteries of any convenient number. The kilns themselves are all alike. Each consists of a shaft, 24, inclosed by end walls 25 and 25 and side walls 26 and 26. A steel jacket 54, may be used to incase the exterior of the kiln walls, but this is not essential if the walls themselves are made fairly air-tight. The end walls are supported on arches 27 and 27, resting on the foundation 28. The side walls 26. .26 rest directly on 28. If-preferred, the shaft may be made circular or elliptical in section, although I do not consider it as desirable asthe rectangular section illustrated.

In the foundation of the kiln is placed a hydraulic ram. 29, the plunger, 30, of which carries a platform 31. The platform is normally in the position shown in Fig. 2 and thus closes the bottom of the kiln against the indraft of an excess of air. Above the arches 2727' are a number of narrow openings 32, 32, respectively. These pass entirely through the respective walls 25, 25, and establish communication between the atmosphere and the shaft 24. Suitable dampers, 33, 33simnle slides as shownserve to regulate the free area of the ports 32, 32 and thus control the quantity of air admitted to the kiln. These ports. 32, also have another and separate function. which is to permit of the insertion of false bars, 34, bridging the shaft 24, and furnish support for the ends of the bars. The function of the bars 34 is to provide a temporary supprrt for the column of bricks or other ware in the shaft 24, during the time occupied in lowering the platform 31 and removing the section of the charge of burned bricks which it-carries. The platform. 31, has deep grooves, 35, which correspond in position with the false-bars 34. and

5 are of a depth slightlv (say about inch) greater than the height of the bars. The width of the flat tops of the bars should be about that of the thickness of a brick. The number of bars should be the sameas the number of bricks required to span the shaft when laid end to end, the bars being so spaced that each comes directlv under the middle of the row of transverse bricks which it supports.

In starting operations a column of previously burned bricks is built up from the platform 31, which then occupies its highest or normal position. The bricks may be laid in checker work, according tothe plan fig- 0 charging brick kilns provided that at uni-.

ured, or according to any plan'now used in form intervals courses are laid which provide longitudinal channels corresponding in vertical position with the ports 32, of suflicient width and depth-to permit of themsertion of the bars 34. The intervals to be observed between these special courses depends principally upon the frequency with vhich the draws are to bemade, andj should correspond to the height of the column of brick (or other ware) that can be completely burned in the time allotted between draws. The number ofcourses of the green brick or ti le (or anyother ware) that may be charged at one time depends upon the strength possessed by the green bricks and should correspond to the number of courses the green bricks are able to bear without.deformation. This may be takenas from four to eight'courses, depending upon the quality of the clay as molded, pressure used in molding the bricks, etc. Therefore, in my preferred method of working I charge several times during the interval between draws keeping, of course, the ag gregate number of courses charged during an interval equal to the niunber of courses drawn at one time. In the plan of laying the brick shown, a uniform arrangement has been observed throughout the charge. As mentioned above, however, by putting in a special course at regular intervals any suitable arrangement may be, used for the intermediate courses.

The shaft 24 having been charged with burned bricks the kiln is in condition to start operations. Producer gas is admitted to the lines 36, 36 by opening the valves; 37, 37. From 36, 36 the gas passes checker work, normally escaping from'the open top of the kiln to the atmosphere. The gas ports 38, 38 are, preferably, built high and narrow, the height in the case of a brick kiln being equal-for the plan of laying the brick shown in the drawingsto two double courses of brick. of open flues through the charge always facing thegas ports. These afford the necessary space for the development of the flame when starting the kiln with a cold charge. If preferred, open combustion chambers may There is therefore a seriesbe built into the kiln walls at the gas ports which will fulfil the same function.

The producer gas is supplied by the gas producer 40, located in the present plan at one end of the battery of kilns. I may use any type of producer in this connection, although I prefer a down-draft type. The air for the producer is supplied by, preferably, a positive pressure blower 41. The discharge pipe of ll is connected to the nozzle of an injector 42. Combustion-gas conduits 43, as, heavily insulated, connect the induction chamber of theinjector with the fines 4%, 14 of each kiln through the connections 4E5, 3L5, respectively. Valves 46,

-16, on and 45, respectively, serveto regulate or entirely out off the connection drawn from the kiln and carried into the producer with th air discharged through the injector 4:2. The draft current of mixed air and products of combustion enters the producer below the grate and passes upward through the bed of fuel therein, In the method of operating the producer which Iprefer I pass the draft current through the fuel bed at such a speed that only part of its carbon dioxid is dissociated. This result may be effected in three different ways. (1) I may work with a comparatively restricted gas making area; (2) I may work with a large gas making area but a limited depth of fuel; or, may work at a temperature so low that the reaction between the carbon of the fuel bed and the CO, of

the draft current takes place only {sluggishly, permitting a comparatively high proportion of the CO to go through unchanged. In this latter case, owing to the low temperature of the fuel bed and the consequent low rate of combustion, it is necessary to provide a relatively large gas makingarea for the producer.

Instead of passing all the-combustion gas withdrawn from the kiln through the ports 48., 48, through the fuel bed of my producer, I may, if I prefer, divide the current of combustion gas into two'portions, adding one portion to the air current supplied-to theproducer in the manner describedabove and the other to the' normal producer gas above-the fuel bed. The result secured is precisely the same as by thefirst procedure, i. 6., a large volume .of modified producer gasof much lower calorific valueper cubic foot than the normal gas but containing a much greater number of B. T. ofpotenair gas'ification of the fuel. air gasificationi in the producer theoretically -one half 'of the total air required for combustion in the system (producer and kiln) tial heat per unit of fuel consumed on the grate. I aim to introduce my combustion gases into the producer at as high a temperature as is consistent with a satisfactory operation of the kiln itself. With this in view, I withdraw my combustion gases at the upper limit'of what may be considered the firing zone proper, where they are at a temperature of, say, 1700 F ah., and conduct them through heavily insulated condui'ts to the gas producer. By introducing the combustion gases into the producer at a high temperature I greatly reduce the net quantity-of heat, in excess of the sensible heat of the gases themselves, which is required to dissociate the CO ofthe combustion-gases, and therefore increase the proportion of combustion gases, which I may supply to the producer.

As is well known to those skilled in the art, the reaction between CO and carbon,

CO +C= CO, is a highly endothermic one.

Themaximum percentage of CO which may be present inthe combustiongases in practice is 20.8, but owing to the necessity ofconducting the combustion with at least a slight excess of air the percentage present seldom reaches 19%. With this percentage of the temperature that must be possessed by the combustion gases at their point of entrance to the fuel bed in order to make the above reaction self-supporting (i. e. in

order to dissociate the CO of the combustion gases without taking heatfrom the fuel bed) is, in practice, about 3200 Fah. Any

deficiencyin the sensible heat carried by the gases below that corresponding to this-temperature must be supplied by the air combustion of the fuel in the producer. By introducing'rmy combustion. gases into my producer at the highest practicable temperature I am able to deliver to my kiln the proper .quantityof CO with the use in the producer of, -much less than thenormal volume of air. Itis tobe noted that the gasification of the .fuel by C0 forms double the volume of CO per unit of .fuel than is given by the When using is introduced into the producer. By my system much the larger proportionof air the producer. This is the .main object, in this present invention, .in introducing the hot combustion gas into theproducer. Incidentally, I am able asa result ofthe use of combustion gases in my producer to operate the j latter at a temperature below the llii possiblein the ordinarymethod of running I clinkering point of the ash of the fuel,but this feature is one which I have already claimed in my Letters Patent 329,105, dated Aug. 21, 1906, and others, and therefore do not claim herein.

As stated above, my object in modifying my producer gas is to "obtain a gas which, without any sacrifice of net calorific value per unit of fuel burned in the producer, will contain sufliclent diluent gas to reduce the temperature developed in its combustion to that desired in burning the ware under treatment. This temperature varies from sa 1700 to sa 2900 accordin to 7 y) 7 y, D

' paratus which 1, herein, reveal, I am able to secure absolute uniformity in the burning of the bricks or other ware. lVith all the methods of burning known to me that are in present use, this result is impossible.

As soon as the heats in the kiln above the level of the gas ports have been brought up to about the normal temperatures I begin the actual operation of the kiln. The valves 5358 on the top gas off-takes 5959 are opened and the eXhauster 60 started. The suction of the eXhauster draws off the combustion gases fromthe upper portion of the shaft through the ports 61-61, the'horizontal cross lines 62-62, the ofi-takes 5959 and the conduits 6363 to the exhauster 60. This exhauster is of 'sufiicient capacity to, not only, draw off the entire volume of products of combustion from the kiln, butto also cause a down-draft of air through the open top of the kiln, enabling the workmen to lay fresh courses on top of the column. Green or unburned bricks (with or without having been subjected to a preliminary drying) are now built onto the column of burned bricks (or other warel originally charged into the kiln. The number of courses laid depends,

as previously mentioned, upon the strength of the green bricks, and is usually from 4: to 8. As the first courses of green bricks are dried by the combustion gases discharg ing from the kiln, additional courses are built onto the column, until there has been laid a number of courses corresponding to the number that is to be drawn. The valve 19 on the pipe of the ram 29 is now jopened and the water in thel cylind'er 51 v of the ram allowed toslowly escape into an accumulator (not shown). The-plunger of the ram 29 sinks gradually against the pressure in the accumulator, the .colhmnof bricks, or other ware, in the kiln.shaft, of course, settling with it. WVhen the column.

has settled a distance corresponding :to the number of courses of green brlcks added to the top of the column the valve 49 is shut and the plunger comes to rest. If the -column has been built up in the manner above specified, when the motion of the plunger has been stopped, there will be open transverse flues in the brickwork corresponding in position to the sets of a1r ports 32-32, The false bars, 34, are now. inserted through the air ports on one side and pushed through the above mentioned fiues or channels until their ends rest on the bottoms of the opposite air ports. The valve 49 is again slightly opened and the plunger with its platform and burden sinks slowly until the bricks of the transverse course above'the bars havecome to rest on the bars. The valve 49 is now closed and the valve 52 on pipe 53 opened,-allowing thev water in cylinder. 51 to escape to a drainl carrying with it that portion of the charge column below the false bars 34. Then the platform 31 has come to rest these bricks. are removed and placed upon acar or con veyer for conveyance 'to'storage. Thevalve 52- havmg been closed when the plunger had reached its lowest position the valve 49- The firing is now continued until the hot gases passing up through the kiln have completed the burning of a fresh sectionbf brick and have'dried the green bricks to an extent that will enable them to bear. the

burden of another series of charges each of a or 8 courses,- as may be, offresh brick.

"When this condition has been attained the pumpbfi, whose suction pipe 56 is con 'nected with the accumulatormentioned? is started and the valve 57 on the discharge pipe of the pump, which pipe is connected into the pipe 50, is opened. Thewater forced into the cylinder .51 raises the plunger 30 with, its platform and burden until the weight of the latter has been lifted off the bars 34. These latter are now avithdrawmthe valve 57 closed and the valve 19 opened, allowing the water in the cylinder 51 to escape to the accumulator as be fore. The column is dropped for the proper number of courses as before, the bars 34 "again inserted, the portion of the column below the bars removed from the kiln, as

before, and the platform 31 again raised to its normal position. The fan 60 is again started, and another series of charges of t The plunger falls,

courses (or whatever number has been de-- cided upon as suitablel of green bricks is built upon the top of the charge, and the operation continued as before.

When all of the original charge of burned brick has been withdrawn, the, kiln has assumed its normal operating condition. In this condition the kiln is filled with bricks (or other ware) in all stages of burning. The latest charged courses are subjected to the action of the comparatively cool combustion gases discharging from the kiln. These, while at a comparatively low temperature, owing to their relatively great volume, rapidly absorb the moisture in the few courses of green bricks on top of the charge. As the bricks are withdrawn at the bottom of the kiln a'nd the charge sinks, the'partially dried bricks are carried farther down into the shaft, where they'are subjected to a current of gas of somewhat higher temperature, and completely dried, while another set of courses of green bricks are built up upon them. After each draw, the, particular lot of bricks whose course we are tracingthrough the kiln, is exposed to gases of increasing temperature until it has been brought up to the previously determined temperature of burning. It now enters and passes through the firing zone, proper,

where it is exposed to the flame of modified producer gas of the selected temperature. As shown in the drawings, the gas ports are high and narrow, the height being equal to two double courses of bricks. There is,- therefore, always a course of bricks laid end on toward the ports presenting clear transverse channels facing the ports, and afford ing a free passage for the flame to the interior of the column of bricks filling the shaft. This results in a very uniform distribution of the flame throughout the column, with the result that all the bricks in the lot are exposed to practically identical conditions. As the bricks pass below the firing zone, they meet the ascending current of heated air which has passed through the previously burned bricks in the lower part or cooler of the kiln. This air, while cooler than the bricks just leaving the firing zone, is stillof such a temperature that there is no sudden chilling effect/exerted upon the bricks, with the resulting brittleness, such as occurs when cold air is admitted to the kiln after drawing the fires in the ordinary method of burning. through the cooler, they are exposed to air of a gradually decreasing temperature, until, upon reaching the bottom of the cooler, they have had their temperature reduced to nearly that of the atmosphere. The heat carried out of the firing zone by the bricks is thus returned to the same by air supplied for the combustion. On the other hand,

. when the hot combustiongases-leave thefir As the bricks sink ing zone and pass through the cooler bricks above'they give up their heat to the latter which, in effect, restore it to the firing zone. 1 am. thus able to secure, in my method of burning, a practically perfect recuperation of both the heat of the combustion gases and that of the burned brick. Moreover, all parts of the chargeare exposed successively to absolutely identical conditions. .Further, the arrangement of my kiln is such that the most favorable possible conditions of treatment are secured. The bricks are first dried by contact with gases of comparatively low temperature, they are then slowly annealed up to the burning temperature, exposed to this temperature for a sutficient length of time tosecure thorough burning, and then gradually annealed down to atmospheric temperature. V I

As mentioned above, I may build in a special course of already burned bricks at each charging designed to engage the falsev The-kilns are all operated in the same manner, the producer, blower, and exhauster being common to the battery of kllns. The various operations of charging and drawing are arranged to take place on the different kilns successively. so that it is possible'to operate a large battery of kilns with one set of workmen. This also permits of a very uniform qualityqof combustion gas being.

supplied to the producer. During the time of drawing a kiln, there is, necessarily, a,

considerable inrush of air at the bottom whichresults inthepresence of a considerable percentage of free oxygen in the combustion gases.) Duringthis period the kiln that is being drawn may be cut off from the fan, andthe'combustion gas supplied to the producer drawn only" from the kilns which are in normal condition. Y

It isfiunderstood that the term modified producer gas as: used in the following claims means a gas made in a gas producer under such conditions that the resultant.

gas designedly contains a more or less abnormal proportion of. diluent gas, the pro portion of said diluent being adjusted to that which will give on the subsequent combustion ofthe gas a flame temperature slightly above the temperature at which it is designed 'to'burn the ceramic material;

Owing to the poorv conducting power of ceramic materials a slight differential muse exist between .the temperature of the flame would give an initial flame temperature of claims l 1900 to LOOO Fall.

It is to be understood, also, that by the term ceramic ware which I use in the mean to include, all varieties of structural bricks and tiles which are subjected to burning as a step in their manufacture as well as paving bricks, fire bricks, terra-cotta ware, pipes, etc.

Having described. my invention, what I claim is 1. The process out burning ceramic war which comprises advancing a column of said ware. through a relatively long substan tially vertical conduit, maintaining a firing zone at an, intermediate region of said conduit, admitting air at the lower part of said conduit and passing the same upward through the interstices of the column of ceramic ware in the lower part of said conduit, which portion of said column has passed through said firing zone, to cool the burned ceramic ware in said portion of said column and to heat saidair, withdrawing combustion gases from a locality of said conduit at the upper part of said firing zone, passing said gases through a comparatively thick bed of ignited fuel to reduce a portion of the carbon dioxid of said gases to carbon. monoxid, re-introducing the so treated gases into said conduit at said firing zone, whereby the combustible matter of said gases is burned in immediate contact with the ceramic ware in that portion of said column occupying said firing zone,

and passing the major portion of the gases from said combustion upwardthrough the interstices of that portion of the said col umn above said firing zone.

2. The process of burning and annealing ceramic ware in a single substantially ,vertical kiln-chamber which consists in contacting the burned ware in the lower part of said chamber with a current of air in counter-current effect, inone end-section of said chamber whereby the said burned ware is cooled and the said air current heated, and burning another lot of ceramic ware in an intermediate part of said chamber by subjecting the said ware to contact with a flame of burning gas in counter-current effect, said gas being derived by contacting gases withdrawn at a comparatively high temperature from the burning zone of said kiln chamber with ignited carbonaceous material to reduce to carbon monoxid that proportion of the carbon dioxid of said gases which will give a gas having a composition such that on burning with said heated air it will give a flame temperature not materially exceeding the selected temperature'of burning.

3. The process of drying, burning and cooling ceramic ware in a single kiln-chains her, which comprises causing the progressive movement of a column of such ware throughsaid chamber, entering a current of air near the place of emergence of said column of ceramic ware from said chamber, causing said air currentto move through the interstices of said column of ceramic '1 re in a direction opposite to the direction of movement of said column, whereby the burned ceramic ware in that portion of said column is cooled and the said air current heated, adding to said heated air current, at a. place in said chamber intermediate between the extremities of said chamber,

producer gas so modified as to give on its combustion with said heated air a flametemperature approximating the, selected temperature for burning said ware, whereby the ceramic ware in the intermediate part of said column is subjected to contact with a burning flame, passing the products of the combustion in said flame through the interstices of the column of ceramic ware in the direction opposite to that of the movement of said column, whereby the ceramic ware in that portion of the column which is approaching the burning zone is heated to substantially thetemperature of burning, and, the said products ofcombustion are partially cooled, and, finally, passing the partially cooled products of combastion through the interstices of that por tion of said column of ceramic ware which contains the green ware, whereby the said green ware is subjected to a gradual drying.

4. The process of'making ceramic ware which consists infeeding said ware downtacting said ware with the hot combustion.

gases from the firing zone of said kiln, burning the dried and heated ware in the said firing zone by means of a flame of modified producer gas, said modified producer gas being formed by withdrawing hot combustion gases from the firing zone of said shaftkiln and passingsaid gases through a .com-

paratively deep bed of fuel at a velocity such that a substantial proportion of the CO of said combustion gases is unreduced,.

and gradually cooling the burned ware by contacting the same with the air current.v

supplied for supporting the combustion of the producer gas.

5. The process. of treating ceramic ware which consists 1n contacting. with ignited;

carbon a portion of the combustion gases produced in the burning of said ware, said gases being withdrawn from the firing zone of said kiln, the temperature of said ignited carbon and the time of contact of said combustion gases therewith, being so regulated that a proportion of the carbon dioxid of said combustion gases will be reduced to carbon monoXid, the proportion of carbon monoxid so formed being that which will give a fiame temperature approximating the temperature selected for burning the said ware on its combustion in said kiln, heating air by contacting the same, in counter-current effect, with previously burned ware, burning said combustible gas with said heated air in contact, in counter-current efi'ect with the ware to be burned, and preparing a fresh lot of ware for burning by contacting with the same the products of combustion from the burning of said gas.

6. The process of treating ceramic ware which comprises, maintaining a column of such ware in a relatively long conduit, maintaining a firing zone at an intermediate region of said conduit, charging raw ware onto the column at one end of said conduit, withdrawing burned ware from the said column at the other end of said conduit, introducing a current of air at the discharge end of said conduit, passing said air through the interstices of that portion of said column approaching the discharge end of said conduit, whereby the burned ware in that portion of said column is cooled and the said air heated, withdrawing a portion of the combustion gases after the same have been used in said firing zone, passing the remainder of said combustion gases through the interstices of that portion of the said column approaching said firing zone, whereby the ware in that portion of said column is subjected to a progressive drying and heating and the said gases are cooled, mixing with the combustion gases withdrawn a regulated proportion of air, contacting the mixture so obtained with ignited carbon to convert a portion of the carbon dioxid of said combustion gases to carbon monoxid, the relative proportions of combustion gases and air, the time of contact of said gaseous mixture with said carbon and the temperature of said carbon being so regulated that the proportion of carbon monoxid produced and the proportion of carbon dioxid left unreduced will be so balanced that the resulting combustible gas will on combustion with i viously dried and heated ware in that por- 7 tion of said column occupying said firing zone is subjected to a flame of the desire temperature. 7

Signed at New York city, in the county of New York and State of New'York, this 27th day of Oct, A. D. 1909.

HENRY L. DOHERTY.

Witnesses:

THOS. I. CART R, C. B. GILBERT.

Copies of this patent'may be obtained for five cents each, by addressing the Commissioner of Patents,

' Washington, D. C. V r 

